Heating Ducts, Ceiling or floor?

[Wildman]

Hi All

In the process of getting gas ducted heating quotes and have a choice of ducting to make. One quote is all ceiling, one is all floor and one is a combination. The combination has floor ducts in the bedrooms and bathroom (under the towel rail, they think of everything) and the living areas have ceiling ducts. The combination is not as bad as expected as it has spare ducts under the house for the future extra bedrooms and there is nowhere for the unit to go outside or under the house so we need ducts top to bottom anyway, but I was after opinions on ceiling vs floor ducts overall. Obviously floor ducts have advantages from a physics perspective, but the missus wants the flexibility to move furniture anywhere she chooses (it seems to happen regularly). Are ceiling ducts ok or do you need heaps of air flow blowing the air down? The return would be floor level so it should heat up eventually but I dont want to put fans in (I took them out as soon as I bought the place).

Cheers
Ben

[Barry_White]

If it is just heating the registers really should be put in the floor. They also should be put under windows to warm the cold air that comes of the glass.

The velocity of heated air doesn't need to be as high as it does for cooling.

They usually put cooling registers in the ceiling

[Sturdee]

As my workshop is built under the house we got the ducting put in the ceiling with vents blowing the air down. Didn't want to have to negotiate heating ducts in the shop. :D :D :D

I haven't noticed any real difference with the ducting above rather than coming from the floor. When it got installed the installer said that at least 40 % of their installations were ceiling based as there often wasn't sufficient room to go below floor level.


Peter.

[Gumby]

Hot air rises anyway. They put floor ducts in under windowes because it's the least likely place to interfere with furniture placement. the best is to install a ceiling fan with reverse switch, set on low speed which circulates the warmer air back down. Put it on reverse for winter so that it sucks air up, across the ceiling and then back down the walls. That way it doesn't matter whether you have them in the ceiling or floor.

[Ian007]

Gday Ben,

i work in the aircon game so i hope this helps

there is no need for ducted gas heating vents to go into the floor unless your ceiling height is over three meters high, heating vents should be placed close to the windows (where possible, depends on roof structure) as this is a major area of heat loss, as you said the return air should be placed at ground level this will enable the heater to work best, and will not cause any heat lock ( all the hot air staying at the top of the rooms) air should throw approx 2.5 meters from a vent dependent on the vent direction.

heating needs at least 5 air changes an hour, refrigerated cooling needs 12 and evap cooling a min of 30 air changes an hour.

this means you need to cube the area of your home and then make sure that the unit will heat this area. this applies to all forms of heating and cooling.
having said that you will probably find that there will not be a big enough gas heater on the domestic market and thats why we put zones into homes and then you only heat the area's in use. (same applies to refrigerated units but you would not normally put zones into an evaporated unit as the volume of air is too high for the zone motors)

and you can get heating vents put into your bathrooms and ensuite if you want as well.
as for the extra future bedrooms would only be a problem if your future extensions are not under the main roof.

hope this makes sense

cheers Ian :)

[Wildman]

Thanks everyone.
I think the ceiling outlets will be the easiest and most flexible (although it is a miserable roof to work in) and we have 2.7m ceilings so not very high. I have just got sizes of the units and am rather unsure how they will get the unit into the roof cavity in the first place,the units I have been quoted on are wider than our roof beam spacing although the Brivis might just squeeze through with enough tiles and battens removed. The brivis unit will do nearly 6 replacements per hour which will give us a bit of spare capacity for the extra bedrooms later on. We wont ever be using the ducting for cooling, we have splits in the bedrooms and living room which do a good job of cooling. One of the guys quoting was quite suprised that I put the splits in myself and that they worked!

Cheers
Ben

[chrisp]

Wildman,

Can you gives us a run down on the installation of the split systems? How did you go about getting the systems gassed?

Chris

[Don777]

Hi Ben

If you are putting in a gas Ducted heating Unit, and if you can put ducting under floor do it. Reason lower outlet velocity, ( less noise ), also better air mixing, ( in ceiling outlet you have to force the mixing ), better positioning of outlets..
One other thing putting the unit outside is general Less noise inside than an in ceiling one

Also the installation and duct layout is the most important thing with ducted heating.

Glad to hear you are looking at a Brivis unit ( hope it is a High Efficency unit)
since I work at Brivis ( well it is now owner by Carrier , since 1999 )

Don

[Wildman]

With the Split installation, I used the gas in the compressor unit to push the air around the head unit and into the lines until gas came out the bleed/vacuum valve. It was in the installation manual as the easy way to install, they did say you could also Vac out the system. I paid $400 + $120 delivery for a 1.5HP Akai split on grays online and putting it in myself saved a heap of cash so if it only lasts a few years I dont really mind and will just get a good quality one when it finally does go. Apparently there is enough gas to do up to 7m of copper (it comes with 3.5m) so you dont have to be too careful not to waste gas doing it this way (within reason). The install is suprisingly easy, the only things required were a drill, holesaw, some large concrete pavers to bolt the compressor to, a 1/2 and 1/4" copper flaring tool (you dont even need them if your compressor is exactly 4m from the head unit), an alan key, a couple of shifters and some pipe shrouding. The kit came with insulated and flared copper tube with brass fittings already, a drain hose and rubber electrical cable. It also had a 15A appliance plug for power and colour coded internal wiring that was a breeze to connect up (it only needed 8A though for either heating or cooling). The head unit had a large mounting plate that was screwed to the wall (few screws in studs, the rest into cavity fixers, it isnt heavy) and the head unit just hooked on. The hole through the wall was cut and the tube and wiring and drain pipe went out making sure the drain pipe could drain, it was connected up outside the wall to the tube supplied, nice and tight (so it doesnt leak!) and the wiring was connected. The gas was let into the system with the alan key opening the taps on the unit. With power supplied and the batteries in the remote it worked first go. The tube and cable was covered with a tin shroud (bought from an air-con suppliers for a few $/m). Definitely better than $600 to install it by a pro. While I am sure vacuuming out the lines may be better, that is the only part of the installation that the average handyman could not do with standard tools. It took me less than 3 hours including laying the pavers in quick set concrete. I did it on a hot night after work in January and had it running before it got dark.

With my central heating, I cant really get the ducts under the floor except under the bedrooms and bathroom as the house is on a slope and the underneath has been dug out and was made in "the pool room" which will eventually become two more bedrooms. For this same reason, there is not really anywhere the heater unit can go outside the house, especially unobtrusively, the only place being suitable is right beside the front door and ducting would still be a misery. All the quoters I have had through have said that it really has to go in the roof. And yes Don, it is a high efficiency brivis (5.1 star) and will have no problems competing against a slightly cheaper 4 star vulcan with lower air flow when it comes to my final decision.

Cheers
Ben

[chrisp]

Ben,

Thanks for the info. I didn't realise that the compressors come pre-charged with gas. Do you know if most other brands come pre-charged?

I've considered buying a split system or two over the years but I have been put off by the installation charge that seems to double the cost of the smaller systems. I've also been assuming that the gas was provided by the installer.

Your response is making me have a think about having a go at the installation :)

Chris